Shells of the said type, in which firing range and effect at the target can be varied have long been known. U.S. Pat. No. 3,306,205, FIG. 1, shows a fin-stabilized shell comprising a firing charge for firing the shell from a launcher, a rocket motor comprising a gas outlet and a rocket motor nozzle for propelling the shell in the trajectory, and an explosive charge for effect at the target. The firing range of the shell and the effect at the target can be varied by the choice of moment for initiation of the rocket motor. Early initiation means that the rocket motor propels the shell for a long period, allowing a long firing range. Late initiation means that the rocket motor propels the shell for a short period, implying a short firing range. The effect of the shell at the target is determined, in the first place, by the explosive effect of the explosive charge, but the final velocity of the shell, i.e. the velocity which the shell reaches at the target, also has an influence. High final velocity means high kinetic energy and high effect at the target, low final velocity means little kinetic energy and minor effect at the target. The rocket motor can thus be used firstly to propel the shell in the trajectory of the shell in order to vary the firing range, and secondly to increase the final velocity of the shell in the final phase of the trajectory and hence increase the effect of the shell at the target.
A drawback with the process is, however, that the rocket motor is not always put to optimum use with regard to firing range and effect. In the case of short firing ranges, when maximum effect at the target is sought and when only a part of the rocket motor is used, the process means that the unused part of the rocket motor is not utilized.